1. Field of the Invention
The present invention is generally directed to a method and system for the downhole injection to an injection formation of surface water and downhole-separated water contained in produced fluids from a production formation of a hydrocarbon well.
2. Background
Produced fluid from hydrocarbon wells can contain a high percentage of water (also referred to as water cut) mixed with hydrocarbon. For example, a large number of oil fields are produced by injecting water to maintain voidage replacement and aid in flooding the oil zone toward the producing wellbore. The wells in these fields tend to produce significant amounts of water. In typical practice, the produced fluids are lifted to the surface where they are processed to separate water from hydrocarbon. The separated water must be subsequently disposed of at the surface or re-injected into a subterranean formation using designated injection wells. As the field matures and water cut increases, operating and disposal costs generally increase while oil production declines.
In many wells, it might be more economical to implement a downhole system to separate the water from the produced fluids in the wellbore instead of producing the produced fluids to the surface, then re-injecting the downhole-separated water into another downhole formation accessible through the same wellbore. Methods for the downhole disposal of water contained in produced fluids have been recently developed. Examples of these methods can be found in patents including WO86/03143; U.S. Pat. Nos. 4,805,697; 5,296,153; 5,456,837; 5,711,374; and 5,730,871; in which separation means are provided downhole to separate the oil and water contained in the produced fluids. These methods rely on downhole pumps to re-inject the downhole-separated water into a suitable zone and to produce the oil to the surface.
Recently, an approach that allows for simultaneous injection of water from surface and hydrocarbon production in a single wellbore was disclosed in U.S. Pat. No. 5,813,469. The apparatus includes a first pump coupled to a second pump. The first pump is powered by pressurized fluid that is injected down the wellbore. The second pump is used to pressurize the produced fluids allowing them to flow to the head of the well and is powered by the first pump. Water contained in the produced fluids flow, together with the hydrocarbon, to the surface.
What is required is a method and system for the downhole separation of water from the produced fluids of a production zone of a hydrocarbon well, and simultaneous injection of the downhole-separated water with surface water, in the same wellbore. Accordingly, the present invention concerns a method and system for the downhole separation of water from the produced fluids of a production zone of a well producing a hydrocarbon and water mixture from an underground formation.
According to an aspect of the present invention, in a well producing a hydrocarbon and water mixture from an underground formation, there is provided a method of separating and injecting downhole water from the produced mixture comprising the steps of delivering surface water to a downhole fluid-driven pump under pressure so as to drive the pump, separating the mixture obtained from the formation into a predominately water component and a predominately hydrocarbon component and directing the predominately water component to the pump, by way of the pump and combining the surface water and predominately water component to obtain a combined fluid. The combined fluid is directed into a downhole injection formation by way of the pump.
In accordance with a preferred embodiment of the present invention, the mixture obtained from the formation is at least 20% water.
In accordance with yet another preferred embodiment of the present invention, surface water is delivered to the downhole pump through the interior of a dedicated tube extending between the surface and the pump. In accordance with yet another preferred embodiment, surface water is delivered to the pump by way of an annular space located within the well.
In accordance with yet another preferred embodiment of the present invention, surface water is pressurized with the use of a pump located at the surface.
In accordance with another preferred embodiment of the present invention, a separator that separates liquids of different densities is used downhole to separate the produced mixture into a predominately water component and a predominately hydrocarbon component.
In accordance with yet another preferred embodiment of the present invention, the downhole separator comprises one or more than one cyclone separator wherein liquids of different densities are separated.
In accordance with yet another preferred embodiment of the present invention, the predominately hydrocarbon component is delivered to the surface of the well through a dedicated tube within the wellbore or through an annular space located within the wellbore.
In accordance with yet another preferred embodiment of the present invention, delivery of the predominately hydrocarbon component to the surface includes the use of an artificial lift system. This artificial lift system may be selected from a group consisting of gas-lift systems, beam pump systems, progressive cavity pump systems, electrical submersible pump systems, and hydraulic pump systems.
In accordance with yet another preferred embodiment of the present invention, the producing formation may be above the injection formation. In another embodiment of the present invention, the producing formation is located below the injection formation.
In accordance with yet another preferred embodiment of the present invention, the separator is located below the producing formation. In accordance with yet another preferred embodiment of the present invention, the separator is located above the producing formation.
In accordance with another aspect of the current invention, there is provided, in a well producing a hydrocarbon and water mixture from an underground formation, a system for the downhole separation and injection of water contained in the produced mixture comprising an oil-water separator for separating the produced mixture into a predominately hydrocarbon component and a predominately water component, and having at least one inlet to receive the produced mixture, at least one outlet for the predominately hydrocarbon component of the mixture to pass from the separator. The system further comprises at least one outlet for the predominately water component of the mixture to pass from the separator; and a downhole fluid-driven pump for receiving surface water under pressure so as to drive the pump and that is in fluid communication with the separator outlet for the predominately water component of the produced mixture to permit combination of the predominately water component and the surface water as a combined fluid, and comprising an outlet oriented to permit direction of the combined fluid into a downhole formation.
In accordance with a preferred embodiment of the invention, the system further comprises a tube extending from the surface of the well to the downhole pump for the delivery of surface water to the pump. This tube can be a dedicated tube which isolates the surface water within the casing of the well or an annular space formed within the casing of the well and in fluid communication with the downhole pump. The annular space need not be perfectly annular in shape.
In accordance with yet another preferred embodiment of the present invention, the system further comprises a pump located at the surface for delivering surface water to the downhole pump under pressure.
In accordance with yet another preferred embodiment of the present invention, the system further comprises a dedicated conduit for delivery of the predominately hydrocarbon component of the produced mixture to the surface. The conduit is in fluid communication with the separator outlet for the predominately hydrocarbon component of the produced mixture and extends to the surface of the well.
In accordance with yet another preferred embodiment of the present invention, the system further comprises an annular space within the wellbore for delivery of the predominately hydrocarbon component of the produced mixture to the surface. The annular space is in fluid communication with the separator outlet for the predominately hydrocarbon component of the produced mixture and extends to the surface of the well.
In accordance with yet another preferred embodiment of the present invention, the system further comprises a water disposal string for delivery of combined fluids from the fluid-driven pump to the injection formation.
In accordance with yet another preferred embodiment of the present invention, an artificial lift system is used to aid in delivering the hydrocarbon component to the surface. In accordance with yet another preferred embodiment of the present invention, the artificial lift system is selected from a group consisting of gas-lift systems, beam pump systems, progressive cavity pump systems, electrical submersible pump systems, and hydraulic pump systems.
In accordance with yet another preferred embodiment of the present invention, the fluid-driven pump is selected from a group consisting of jet pumps, progressive cavity pumps, turbine pumps, and reciprocating pumps.
In accordance with yet another preferred embodiment of the present invention, the fluid-driven pump comprises a pump and a motor.
In accordance with yet another preferred embodiment of the present invention, the oil-water separator comprises one or more cyclones housed in one or more than one separator, the cyclones acting in parallel or in series.
In accordance with yet another preferred embodiment of the present invention, the fluid-driven pump is located inside the same housing as the oil-water separator.
With the method and system of the present invention, surface water and downhole-separated water is injected downhole with the use of a downhole fluid-driven pump that uses surface water as a power fluid. Hydrocarbon is brought to the surface either naturally under the eruptive force of the production zone, or with the assistance of regular artificial lift methods such as gas-lift. With the present system, downhole-separated oil and surface water can be transported through the wellbore in either a conduit or annular space located within the wellbore. This variable tubing configuration allows for optimizing the flow of fluids in the wellbore. Potential benefits of this invention includes increased hydrocarbon production, reduced operating costs due in part to reduced power consumption and reduced handling of water at the surface; reduced capital costs by alleviating the need to drill separate wells for downhole injection of water; and improved oil-water separation conditions by locating the oil-water separator downhole. Another advantage of the present invention is the use of a single fluid-driven pump downhole. Such pumps can be more reliable than electrical pumps and mechanical pumps downhole and do not require rod or cable connections to surface.
Other and further advantages and features of the invention will be apparent to those skilled in the art from the following detailed description thereof, taken in conjunction with the following drawings.